Un-ciphered network operation solution

ABSTRACT

The present invention relates to a solution for handling security issues of non access stratum (NAS) signaling in a telecommunications network. The NAS signaling is performed between a user equipment (UE) and a mobility management node, e.g. a mobility management entity (MME). The solution is realized in a device and in a method comprising steps of receiving an initial non access stratum message from the UE communicating wirelessly with the telecommunications network, determining security context status for the UE, determining if un ciphered mode is to be used in the security context, set ciphering algorithm to a null ciphering algorithm, transmitting a security context and activation message to the UE, comprising information indicating ciphering algorithm, and receiving a security context activation acknowledge message from the UE.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/201,500 (now U.S. Pat. No. 8,626,122), which is a 35 U.S.C. 371National Phase Entry Application from PCT/EP2010/051105, filed Jan. 29,2010 (published as WO 2010/091966), which designated the U.S. and claimspriority to U.S. provisional patent application No. 61/152,817, filedFeb. 16, 2009. Each of the above identified applications andpublications is incorporated by reference.

TECHNICAL FIELD

The present invention relates to a solution for handling security issuesof non access stratum signaling in a telecommunications network.

BACKGROUND

The NAS protocol used for UE/MME interaction has a security protectionmechanism comprising integrity protection and/or ciphering of messages.In normal ciphered operation all messages shall be ciphered as soon as asecurity context has been activated for a specific NAS connection.

It is also specified in 3GPP TS 24.301 that ciphering is an operatoroption. Thus SAE needs to support un-ciphered operation in the NASprotocol.

Different methods to solve un-ciphered operation may be selected and oneway is to always use non security protected NAS messages. There are twogeneral types of NAS messages, plain NAS messages that have no securityprotection and security protected NAS messages that have integrityprotection and/or ciphering applied.

If there is no common way to solve un-ciphered operation mode in SAEthere will be interoperability problems between UE and MME and betweendifferent vendors, effectively making un-ciphered operation impossible.

If a method is chosen where non security protected NAS messages are usedfor all messages in un-ciphered operation mode, it implies that the MMEimplementations will be more complicated and needs to be able todistinguish between ciphered and un-ciphered operation for most NASmessages.

Furthermore, if using plain NAS messages in un-ciphered operation,integrity protection of the NAS messages will not be available andexceptions to those rules would also have to be implemented.

SUMMARY

It is therefore an object of the present invention to address theseproblems and to provide a solution for interoperability of NAS security.

The concept of the present invention is to select a “null cipheringalgorithm” when a security context is selected for use by a mobilitymanagement device, e.g. a Mobility Management Entity (MME) operating inun-ciphered mode. This may be done for all UEs using the network inun-ciphered operation or for individual UEs in connection with the MME.In all other aspects the NAS messages may be sent, received, and treatedin the same way as in a network in normal ciphered operation.

This is provided in a number of aspects of the present invention, inwhich a first is a method for handling security issues in aninfrastructure node in a telecommunications network. The methodcomprising the steps of: a) Receiving an initial non access stratum,i.e. NAS, message from a user equipment (UE) communicating wirelesslywith the telecommunications network; b) Determining security contextstatus for the UE; c) Determining if un-ciphered mode is to be used inthe security context; d) Set ciphering algorithm to a null cipheringalgorithm; e) Transmitting a security context and activation message tothe UE, comprising information indicating ciphering algorithm; and f)Receiving a security context activation acknowledge message from UE.

All security contexts may be created with a null ciphering algorithmand/or security context for individual UEs may be set to a nullciphering algorithm.

The method may further comprise steps of receiving further NAS messagesand deciphering the further NAS messages using the null cipheringalgorithm. Furthermore, the method may also comprise a step of providingintegrity protection of communication messages. Messages may be treatedas being in normal ciphered mode independent on ciphering mode.

The null ciphering algorithm is preferably arranged so as to operate onmessages in such a way that the messages are un-altered.

The step of transmitting security context may include indicating in afield in a message one of no integrity protection and no ciphering,integrity protection only, or integrity protection and ciphering on.

Another aspect of the present invention is provided, an infrastructuredevice in a telecommunications network. The device comprising aprocessing unit, a memory unit, and a communication interface unit. Theprocessing unit may be configured to execute instructions sets stored inthe memory unit for receiving using the communication interface aninitial non access stratum, i.e. NAS, message from a user equipment,determining security context status, creating a new security context,determining if un-ciphered mode is to be used in the security context,set ciphering algorithm to null, transmitting, using the communicationinterface, a security context and activation message to the UE,comprising information indicating ciphering algorithm, and receiving,using the communication interface, a security context activationacknowledge message from UE.

The infrastructure device may be a mobility management device, e.g. amobility management entity (MME).

With the solution according to the present invention the followingadvantages may be realized: the criteria for accepting a particular NASmessage may be the same in ciphered and un-ciphered operation; theintegrity protection part of security protection may still be active inun-ciphered operation; and the solution may be entirely implemented inthe MME—i.e. no UE impact; which thus provides a cost efficientimplementation of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in a non-limiting wayand in more detail with reference to exemplary embodiments illustratedin the enclosed drawings, in which:

FIG. 1 illustrates schematically a network according to the presentinvention;

FIGS. 2A and 2B illustrate schematically a device according to thepresent invention;

FIGS. 3A and 3B illustrate a method according to the present invention;and

FIG. 4 illustrates schematically in a block diagram another methodaccording to the present invention.

DETAILED DESCRIPTION

In FIG. 1, reference numeral 100 generally denote a telecommunicationsnetwork comprising a radio access network 102 in connection 106 with amobility management device 103, e.g. a mobility management entity (MME),which is part of a core network 104. The radio access network providesaccess to the telecommunications network for user equipment 101 (UE)connecting wirelessly 105 to the radio access network, for instance viaa base station (not shown), e.g. an eNodeB or similar network accessnode. For illustrative purposes the MME will be used in the descriptionbut it should be noted that other mobility management devices may beapplicable. The network may comprise further nodes; however, these arenot shown since they do not form part of the present invention, forinstance a serving gateway, a packet data network gateway, a homesubscriber server, and so on. Furthermore, the network also comprisescommunication distribution devices such as routers, switches, andcabling for physical distribution of communication data.

The UE attaches to the network using normal attachment proceduresdepending on protocol standard in use, e.g. LTE, SAE, or similar packetbased protocols. During attachment to the network the UE is to establisha non access stratum connection to the core network 104. This isinitiated by the UE which sends a request for establishment to the corenetwork and to the MME.

When a new NAS connection is established between the UE and the MME asecurity context shall be taken into use and this is negotiated betweenthe UE and the MME. If the MME has been configured not to applyciphering for NAS messages the MME selects a “null ciphering algorithm”to be used by the security context. Apart from this exception the MMEmay handle all procedures and NAS messages between the UE and the MME asif the network was operating in normal ciphered mode, i.e. the samerules apply when a particular NAS message shall be marked as “plain” or“security protected”.

The null ciphering algorithm may comprise an algorithm that does notchange the data during encryption. This may be defined in the algorithmitself or by the use of key set identifiers used in seeding thealgorithm making the algorithm perform as not changing the data duringencryption.

Normal authentication procedures may be executed, for instance forintegrity protection of data transmitted. This allows for integrityprotection of data together with null ciphering of data.

The solution according to the present invention is advantageouslyimplemented in the mobility management device, e.g. the MME. The MME103, 200 may comprise, as is seen in FIG. 2A, at least one processingunit 201, at least one computer readable storage medium, e.g. a memoryunit, 202, and at least one communication interface 203. The processingunit is configured to read software or hardware instruction sets fromthe memory unit and together with the communication interface executemethods according to the present invention. The processing unit maycomprise any suitable processing device such as for instance amicroprocessor, central processing unit (CPU), digital signal processor(DSP), application specific integrated circuit (ASIC), or fieldprogrammable gate array (FPGA). It should be noted that the instructionsets may also comprise hardware instructions as usually implemented forASIC solutions. Furthermore, the memory unit may comprise a volatile ornon-volatile memory type or a combination of these types. Thecommunication interface is preferably configured to communicate in apacket based manner, e.g. through protocols such as Internet Protocol(IP) based protocols.

Functional elements of the MME is shown in FIG. 2B where the processorhas a receiving portion for receiving communication data from thecommunication interface, a decision portion for executing softwarecommands for handling decisions related to the operation of the MME andin particular of handling decision related to the security context aswill be described below in more detail. The processor also has atransmitting portion configured to transmit messages via thecommunication interface. All portions of the processor may use thememory unit for temporary storage of data and/or for permanent storageof data depending on configuration of the node.

During operation the MME will communicate with the UE and with otherdevices for operation of network related provisions. For instance aswill be discussed below, the MME participates in establishmentprocedures when a UE attaches to a network; for instance at initialconnection or during hand over from another network.

FIG. 3A and FIG. 3B together illustrate an example of initial NASestablishment procedure. The UE first initiates the establishment bytransmitting 301 an initial NAS message requesting establishment whichis received 302 by the MME. In the next step, the MME checks 303 if asecurity context needs to be created. Depending on if a security contextis to be created or not different paths will be executed. If no newsecurity context need to be created it is decided 304 to use an existingsecurity context and the security context is transmitted 309 to the UE;however, if a security is to be created, it is created 305. Furthermore,the MME checks 306 if un-ciphered mode is to be used; if an un-cipheredmode is used, the ciphering algorithm is set to null 308; otherwise theciphering algorithm is set 307 as chosen. A message is sent 309 toactivate the chosen security context and this is received 310 by the UE.

The UE activates 311 the security context and invokes 312 the cipheringalgorithm indicated in the security message. The UE sets 313 theciphering indicator in an acknowledge message header to true andtransmits 314 the activation acknowledge message to the MME whichreceives 315 the security context activation acknowledge message.

FIG. 4 illustrates a continued action of a communication link between asender, e.g. the UE, and a Receiver, e.g. the MME, when the initial NASestablishment procedure has been executed. The UE invokes 401 theciphering algorithm indicated in the security context and sets 402 aciphering indicator in a message header to true. The UE then sends 403the message which is received 404 by the MME. The MME decipher 405 themessage using the ciphering algorithm indicated in the security contextand finally interpret 406 the message accordingly. It should beappreciated that the communication may be performed in any direction andthat other nodes may be involved in NAS communication with the UE thenthe MME.

It should be noted that the selection of un-ciphered mode may be done atany time, not only when creating a security context. If un-ciphered modeis selected at a certain point in time also the already attached UE'smay get the selected ciphering algorithm changed to null. Also theun-chiphered mode may be turned off at any time by selecting a “normal”ciphering algorithm. Changing the ciphered mode may be used for instancefor tests of UE connection to the infrastructure network or tests of theUE condition.

It should be noted that the word “comprising” does not exclude thepresence of other elements or steps than those listed and the words “a”or “an” preceding an element do not exclude the presence of a pluralityof such elements. It should further be noted that any reference signs donot limit the scope of the claims, that the invention may be at least inpart implemented by means of both hardware and software, and thatseveral “means” or “units” may be represented by the same item ofhardware.

The above mentioned and described embodiments are only given as examplesand should not be limiting to the present invention. Other solutions,uses, objectives, and functions within the scope of the invention asclaimed in the below described patent claims should be apparent for theperson skilled in the art.

ABBREVIATIONS

EPS—Evolved Packet System

LTE—Long Term Evolution

MME—Mobility Management Entity

NAS—Non Access Stratum

SAE—System Architecture Evolution

UE—User Equipment

REFERENCES

[1] 3GPP TS 33.401: “3GPP System Architecture Evolution; Securityarchitecture”.

[2] 3GPP TS 24.301: “Non-Access-Stratum (NAS) protocol for EvolvedPacket System (EPS); Stage 3”.

1. A method for handling security issues in an infrastructure node in atelecommunications network, the method comprising: receiving an initialnon access stratum (NAS) message from a user equipment (UE)communicating wirelessly with the telecommunications network; afterreceiving the initial NAS message, determining that un-ciphered mode isto be used in a security context; in response to determining thatun-ciphered mode is to be used, i) selecting a ciphering algorithm froma set of predefined ciphering algorithms and ii) after selecting theciphering algorithm, transmitting to the UE a message comprisinginformation identifying the selected ciphering algorithm; and receivingfrom the UE a security context activation acknowledge message.